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scarceller scarceller is offline
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Join Date: Oct 2006
Location: Southern MA
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Originally Posted by patkeefe View Post
I am likely going to change my SC turbo to Megasquirt II, maybe next year. I have found over the years that it is not so simple to effectively double the HP output of a N/A system by simply trying to imitate a 930 setup, although I almost have it figured out.

Fundamantally, there are really no differences in the K-Jet and the more advanced electronic systems. It seems to me that the CIS is a bit more stone age with regard to tuning. The Bosch engineers built the CIS system to get away from carbs, which allowed more easy compliance to environmental regulations. However, the K-Jetronic is both technically advanced for something designed over 40 years ago, and elegant in its simplicity from a tuning standpoint.

The main differences in between CIS and any of the other systems are simple to see:
All of the modern tuning parameters were BUILT IN to the hardware of the CIS system. For instance, the shape of the air cone matters, as I believe that is what provides the idle and enrichment characteristic of the particular setup. This is done by some sort of tuning tweaks in the EFI systems. It is theoretically much easier to change parameters in an EFI system than in a K-Jetronic system. There are some interesting and comprehensive discussions on this board regarding this topic. Relationships between the WUR and FD seem simple, because the factory MATCHED these characteristics for each particular engine setup type.

I suppose when you have a CIS system, and get the car shaken out fairly well, there is absolutely no need to go any further. If you want to continue to tinker and try and wring out that last 3 HP, go ahead. There is always going to be the CIS camp and the EFI camp.
All your points on fueling are correct that CIS vs EFI fueling really isn't that different. But ignition is very diffrent between the 2 systems. In EFI you have complete control of ignition setting down to 0.7deg or even better and across the entire RPM range and the entire load range. Then you also have the ability to alter ignition based on other factors like Intake Air Temp and Cyl Head Temp. It's this area of EFI that really stands out when compared to an old school distributor.

Here's a sample Part Throttle ignition table from a 3.2L car:

The rows are injector pulse width in Milliseconds and notice that at very light loads it's running better than 50 degrees advance, you can't set things like this with an old school distributor.
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1984 911 Carrera Cab M491 (Factory Wide Body)
1975 911S Targa (SOLD)
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1987 Ford Mustang LX 5.0 Convertible
Old 11-18-2014, 10:10 AM
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